BERLIN/MOSCOW, Nov 29 (Reuters) - Ukrainian President Petro Poroshenko on Thursday accused Russia's Vladimir Putin of wanting to annex his entire country and called for NATO to deploy warships to a sea shared by the two nations.

Poroshenko's comments to German media were part of a concerted push by Kiev aimed at gaining Western support for more sanctions against Moscow, securing tangible Western military help, and rallying opposition to a Russian gas pipeline that threatens to deprive Ukraine of important transit revenue.

His Western allies have so far not offered to give him any of these things soon, despite his warnings of a possible invasion by Russia after Moscow seized three Ukrainian naval ships and their crews on Sunday.

Moscow and Kiev blame each other for the Black Sea incident, which took place off Russian-annexed Crimea.

"Don't believe Putin's lies," Poroshenko told Bild, Germany's biggest-selling paper, comparing Russia's protestations of innocence in the affair to Moscow's 2014 denial that it had soldiers in Crimea even as they moved to annex it.

"Putin wants the old Russian empire back," he said. "Crimea, Donbass, the whole country. As Russian Tsar, as he sees himself, his empire can not function without Ukraine. He sees us as his colony."

Volodymyr Omelyan, Ukraine's infrastructure minister, on Thursday accused Russia of imposing a de facto blockade on two Ukrainian ports on the Sea of Azov by barring ships from leaving and entering the sea via the Russian-controlled Kerch Strait.

The Kremlin denied it was restricting shipping, saying it had not heard of any problems. If there were any delays they were due to bad weather rather than politics, it said.

Poroshenko told Bild he also wanted NATO to deploy warships to the Sea of Azov. There was no immediate reaction from the alliance, which has condemned Russia's seizure of the Ukrainian ships. The Kremlin said Poroshenko's request looked designed to cause more tensions in the area.

'FORTRESS CRIMEA'

There were further signs that Russia was pressing ahead with its plans to fortify Crimea and turn it into what Kremlin-backed media have called a fortress.

Citing a Crimean security source, Interfax news agency also reported Russian plans to build a new missile early-warning radar station in Crimea next year that would be able to track ballistic and cruise missiles from a long distance.

Russia was also working on a new technical system to allow it to better track shipping around the peninsula in order to protect its maritime borders, Interfax said.

The United States and the EU have both imposed sanctions on Russia over its conduct towards Ukraine since 2014, when Moscow seized and annexed Crimea after a pro-Russian leader was toppled in Kiev.

Moscow later backed pro-Russian separatists in eastern Ukraine in a conflict in which more than 10,000 people have been killed. Major fighting ended with a 2015 ceasefire but deadly exchanges of fire are still frequent.

Poroshenko, whom Putin has accused of manufacturing the Black Sea crisis to boost his flagging ratings before an election next year, called on Germany to halt an undersea pipeline project that would allow Russia to supply more gas to Germany directly.

The Nord Stream 2 project is a potentially serious problem for Ukraine which currently earns large transit fees from piping Russian gas to Europe and stands to lose out.

But Germany's economy minister dismissed the idea that his country's commitment to the pipeline undermined efforts to de-escalate the Ukraine crisis.

"These are two separate questions," Peter Altmaier told the ARD public broadcaster.

Poroshenko's attempts to get the EU to impose new sanctions on Russia appeared to be falling flat.

Heeding his suggestion, the EU's hawks have called for more sanctions but the divided bloc is not going to act swiftly, if at all, diplomatic sources have said.

German Chancellor Angela Merkel said she would raise the Black Sea issue with Putin at a G20 summit which starts in Argentina on Friday where the Russian leader is also due to hold talks with U.S. President Donald Trump.

NATO has urged Russia to release the three Ukrainian navy ships and their crews, saying there was no justification for Moscow's actions. But the military alliance, which Ukraine one day hopes to join, has stopped short of offering to deploy new forces in the area to deter Russia. (Additional reporting by Tom Balmforth and Andrey Ostroukh in Moscow, Michelle Martin in Berlin and Pavel Polityuk in Kiev Writing by Andrew Osborn Editing by Richard Balmforth)